(i) FIELD OF THE INVENTION
The present invention relates to a method for testing a gas diffusion by simulating gas diffusion situations of nature on a laboratory scale, and an apparatus for this method.
(ii) DESCRIPTION OF THE PRIOR ART
Smoke discharged from chimneys and exhaust pipes of tunnels, heat taken out from cleaning towers and gases leaked out through LNG tanks are diffusively blown in a wind. In the case of simulating this phenomenon of nature in a laboratory, a wind tunnel is usually employed. Accordingly, for the simulation, the wind tunnel is provided in its interior with a topography model having chimneys, mountains, rivers and buildings and the like thereon.
Through the wind tunnel thus constituted, a wind is caused to flow, and a specific gas, e.g., a tracer gas is discharged from the miniature chimneys. At this time, an expansion of the gas is observed and measured by a color change test, a suction/gas analysis with the aid of a traverse, and the like.
In this case, for the purpose of accurately simulating the wind direction and the wind velocity, the topography model is rotatably disposed in the wind passage of the wind tunnel. According to the topography model, a gas diffusion test can be carried out by previously establishing the time distribution of the direction and the velocity of the wind blowing above the central portion of its rotation and rotating the topography model on the basis of the established time distribution.
Now, the test method just mentioned will be described in reference to FIGS. 2, 12 to 14 attached hereto.
In FIG. 14, an air flow 1 which has been generated by an air blower not shown and which has been rectified into a steady flow is blown into a wind passage 2 of a wind tunnel. A floor surface 3 of this wind passage 2 is provided at its central portion with a turntable 4 which is rotatably supported by a rotatable support device 12, the top surface of the turntable 4 being at the same level as the floor surface 3. In the vicinity of the center of this turntable 4, a miniature chimney 5 is planted through the turntable 4. Further, a topography model 6 comprising a building and the like is arranged on the turntable 4.
A circumferential plate 9 is projectively disposed under the turntable 4 and is further immersed at its end portion in a sealing liquid 10 pooled in a circumferential groove member 8, which is attached to the circumferential edge of an opening formed in the floor surface 3.
Therefore, a space 11 between the floor surface 3 and the sealing liquid 10 is sealed with the latter so as to prevent air from leaking out therethrough. The turntable 4 can be rotated by a suitable means which is not shown, and a tracer gas 7 is discharged from the miniature chimney 5.
A wind velocity of the wind which blows above the topography model 6 provided on the turntable 4 and a rotation angle of the turntable 4 can be decided as follows: That is to say, the direction and the velocity of the blowing wind are observed during one day on a chimney-disposed site or a construction-planned site to prepare such a wind rose as in FIG. 2, and the rotation angle of the turntable 4 and the velocity the blowing wind are regulated so as to reproduce the wind direction and the wind velocity of the wind rose.
Smoke from the chimney or an exhaust nozzle of the tunnel and heat from a cleaning tower is generally blown up in the atmosphere, rises once and then flows leeward on the wind while diffused. Accordingly, an expansion of the exhaust smoke must be tested and measured by discharging the gas 7 corresponding to the exhaust smoke from a discharge opening 17 disposed at an effective chimney height (He=Ho +.DELTA.H) of a height Ho of the miniature chimney itself 5 plus the total height .DELTA.H of a height h1 of the upward blown smoke and a height h2 of the floatingly rised smoke. It is known that the height .DELTA.H varies, as shown in FIG. 13, with smoke discharge conditions (a velocity of the upward blown smoke and a discharge flow rate) and the wind velocity. As a formula for representing the rise of the smoke, for example, the Bosanquet formula is already put into practice.
In the case of a conventional manner, the height of the miniature chimney is decided on the basis of a reduced scale rate of the topography, and thus it is impossible to carry out the diffusion tests at the variously changed discharge heights.
In general, the wind tunnel is fixed and the topography model in the wind passage also is stationary. Therefore, in the one test, the gas diffusion can only be tested and measured under a specific condition such as the blow of a south wind.
If the diffusion test is contemplated under the condition of a north wind in succession to the condition of the south wind, the topography model must be turned reversely in the wind tunnel. On this topography model, however, there are disposed a pipe for feeding the gas to the miniature chimney therethrough, a pipe for sucking the gas therethrough and the like, and thus returing the topography model reversely is difficult.
Consequently, in any conventional technique, each gas diffusion test must be carried out under each wind direction/wind velocity condition.
As understood from a wind indicator provided on a roof which we often see, the direction of the natural wind is not constant even for a short period of time, and the wind direction alters in an extensive range even for several hours.
When observed in detail, it will be perceived that not only the wind direction but also wind velocity also changes. Accordingly, the gas diffusion test taking the wind direction and the wind velocity in consideration is rightly necessary, but such a test has not be carried out heretofore. In addition thereto, a conventional apparatus for the gas diffusion test also is poor in reproducibility of the test conditions.